I have a table with the following attributes:
MyTable:
- double longitude
- double latitude
- varchar place_id
- varcar geoJSON_string
Given some point having a longitude x and latitude y I need to select the k closest points.
I know I tack a LIMIT k on the end of the query, but is there a way I can guarantee at least k points from a database of ~250,000 records?
Also, how would I even query the decimal values? I need to select something similar to the following:
SELECT * FROM MyTable WHERE latitude=140.3**** and longitude=132.2**** LIMIT k;
SELECT * FROM MyTable WHERE latitude BETWEEN '140.3' AND '140.4' AND longitude BETWEEN '132.2' AND '132.3' LIMIT k;
or, if you need the best result :
SELECT * FROM MyTable ORDER BY ABS(ABS(searched-lon - longitude) - ABS(searched-lat - latitude)) ASC LIMIT k;
Related
I'm not particularly knowledgeable about MYSQL queries and optimising them, so I require a bit of help on this one. I'm checking a table of international cities to find the 10 nearest cities based on the longitude and latitude values in the table.
The query I'm using for this is as follows:
SELECT City as city,
SQRT(POW(69.1 * (Latitude - 51.5073509), 2) +
POW(69.1 * (-0.1277583 - Longitude) * COS(Latitude / 57.3), 2)) AS distance
from `cities`
group by `City`
having distance < 50
order by `distance` asc
limit 10
(The longitude & latitude values are obviously placed dynamically in my code)
sometimes this can take around 3-4 mintues of my development environment to complete.
Have I made any classic mistakes here, or is there a much better query I should be using to retrieve this data?
Any help woould be greatly appreciated.
Assuming City is unique and you are abusing GROUP BY and HAVING in order to get a cleaner code
SELECT City as city,
SQRT(POW(69.1 * (Latitude - 51.5073509), 2) +
POW(69.1 * (-0.1277583 - Longitude) * COS(Latitude / 57.3), 2)) AS distance
from `cities`
where SQRT(POW(69.1 * (Latitude - 51.5073509), 2) +
POW(69.1 * (-0.1277583 - Longitude) * COS(Latitude / 57.3), 2)) < 50
order by `distance` asc
limit 10
If City is unique then the aggregation is done on single rows.
MySQL uses sort operation to implement GROUP BY.
Sort complexity is O(n*log(n)), so without indexes this is going to complexity of GROUP BY.
If City is not unique than the filtering in the HAVING CLAUSE is done on one arbitrary row which is for sure not what the OP intended.
The case where HAVING and WHERE are both relevant for filtering and HAVING has an performance advantage is where the filtering is done on the aggregated column, there are some heavy calculations and the GROUP BY operation significantly reduce the number of rows
select x,... from ... group by x having ... some heavy calculations on x ...
I am trying to calculate and return the distances between some points.
Here is the complete MYSQL statement that I am using. I have tried multiple versions of this formula, and they all have similar results: returning zero result. Any thoughts on what I am doing wrong?
SET #origLat = 37.386337;
SET #origLon = -122.085823;
SET #dist = 20;
SELECT user_id, user_lat, user_lon, 3956 * 2 *
ASIN(SQRT( POWER(SIN((#origLat - abs(user_lat))*pi()/180/2),2)
+COS(#origLat*pi()/180 )*COS(abs(user_lat)*pi()/180)
*POWER(SIN((#origLon-(user_lon))*pi()/180/2),2)))
AS distance
FROM myTable
WHERE user_lon BETWEEN (#origLon-#dist/abs(cos(radians(#origLat))*69)) AND (#origLon+#dist/abs(cos(radians(#origLat))*69)) AND
user_lat BETWEEN (#origLat-(#dist/69)) AND (#origLat+(#dist/69))
HAVING distance < #dist ORDER BY distance LIMIT 100
Here is what is in my table.
Running just my SELECT clause shows that Distance is return nil.
SELECT city, (6372.797 * acos(cos(radians({$latitude})) * cos(radians(`latitude_range`)) * cos(radians(`longitude_range`) - radians({$longitude})) + sin(radians({$latitude})) * sin(radians(`latitude_range`)))) AS distance FROM cities WHERE active = 1 HAVING distance > 25 ORDER BY distance ASC
I like to be able to grab all cities HAVING a distance greater than 25KM and less than 50KM. Anything I try entering either results in all cities greater than 25KM or an error.
How does one go about adding HAVING distance > 25 AND distance <= 50 to my SQL query?
Exactly the way that you have in the question:
SELECT city, (6372.797 * acos(cos(radians({$latitude})) * cos(radians(`latitude_range`)) * cos(radians(`longitude_range`) - radians({$longitude})) + sin(radians({$latitude})) * sin(radians(`latitude_range`)))) AS distance
FROM cities
WHERE active = 1
HAVING distance > 25 and distance <= 50
ORDER BY distance ASC;
Just as a small note: the use of the having clause to filter on column aliases (like distance) is a MySQL extension. In most databases, you would have to use a subquery.
I'm trying to generate some dummy records in MySQL and need to create random latitude and longitude float values within a given range.
For example I need to generate latitudes that are between 52.077090052913654 and 52.477040512464626
and longitudes between -1.8840792500000134 and -0.9172823750000134
I'm familiar with creating ranges of random numbers using Rand Floor but that will only produce whole numbers. How I might do this?
You can use RAND() to get a random value between two values like so:
randVal = (RAND() * (maxVal - minVal)) + minVal
With your numbers:
SELECT
(RAND() * (52.477040512464626 - 52.077090052913654)) + 52.077090052913654 AS randlatitude,
(RAND() * (-0.9172823750000134 - -1.8840792500000134)) + -1.8840792500000134 AS randlongitude
I'm using following sql code to find out 'ALL' poi closest to the set coordinates, but I would want to find out specific poi instead of all of them. When I try to use the where clause I get an error and it doesn't work and this is where I'm currently stuck, since I only use one table for all the coordinates off all poi's.
SET #orig_lat=55.4058;
SET #orig_lon=13.7907;
SET #dist=10;
SELECT
*,
3956 * 2 * ASIN(SQRT(POWER(SIN((#orig_lat -abs(latitude)) * pi()/180 / 2), 2)
+ COS(#orig_lat * pi()/180 ) * COS(abs(latitude) * pi()/180)
* POWER(SIN((#orig_lon - longitude) * pi()/180 / 2), 2) )) as distance
FROM geo_kulplex.sweden_bobo
HAVING distance < #dist
ORDER BY distance limit 10;
The problem is that you can not reference an aliased column (distancein this case) in a select or where clause. For example, you can't do this:
select a, b, a + b as NewCol, NewCol + 1 as AnotherCol from table
where NewCol = 2
This will fail in both: the select statement when trying to process NewCol + 1 and also in the where statement when trying to process NewCol = 2.
There are two ways to solve this:
1) Replace the reference by the calculated value itself. Example:
select a, b, a + b as NewCol, a + b + 1 as AnotherCol from table
where a + b = 2
2) Use an outer select statement:
select a, b, NewCol, NewCol + 1 as AnotherCol from (
select a, b, a + b as NewCol from table
) as S
where NewCol = 2
Now, given your HUGE and not very human-friendly calculated column :) I think you should go for the last option to improve readibility:
SET #orig_lat=55.4058;
SET #orig_lon=13.7907;
SET #dist=10;
SELECT * FROM (
SELECT
*,
3956 * 2 * ASIN(SQRT(POWER(SIN((#orig_lat -abs(latitude)) * pi()/180 / 2), 2)
+ COS(#orig_lat * pi()/180 ) * COS(abs(latitude) * pi()/180)
* POWER(SIN((#orig_lon - longitude) * pi()/180 / 2), 2) )) as distance
FROM geo_kulplex.sweden_bobo
) AS S
WHERE distance < #dist
ORDER BY distance limit 10;
Edit: As #Kaii mentioned below this will result in a full table scan. Depending on the amount of data you will be processing you might want to avoid that and go for the first option, which should perform faster.
The reason why you cant use your alias in the WHERE clause is the order in which MySQL executes things:
FROM
WHERE
GROUP BY
HAVING
SELECT
ORDER BY
When executing your WHERE clause, the value for your column alias is not yet calculated. This is a good thing, because it would waste a lot of performance. Imagine many (1,000,000) rows -- to use your calculation in the WHERE clause, each of those 1,000,000 would first have to be fetched and calculated so the WHERE condition can compare the calculation results to your expectation.
You can do this explicitly by either
using HAVING (thats the reason why HAVING has another name as WHERE - its a different thing)
using a subquery as illustrated by #MostyMostacho (will effectively do the same with some overhead)
put the complex calculation in the WHERE clause (will effectively give the same performance result as HAVING)
All those will perform almost equally bad: each row is fetched first, the distance calculated and finally filtered by distance before sending the result to the client.
You can gain much (!) better performance by mixing a simple WHERE clause for distance approximation (filtering rows to fetch first) with the more precise euclidian formula in a HAVING clause.
find rows that could match the #distance = 10 condition using a WHERE clause based on simple X and Y distance (bounding box) -- this is a cheap operation.
filter those results using the formula for euclidian distance in a HAVING clause -- this is an expensive operation.
Look at this query to understand what i mean:
SET #orig_lat=55.4058;
SET #orig_lon=13.7907;
SET #dist=10;
SELECT
*,
3956 * 2 * ASIN(SQRT(POWER(SIN((#orig_lat -abs(latitude)) * pi()/180 / 2), 2)
+ COS(#orig_lat * pi()/180 ) * COS(abs(latitude) * pi()/180)
* POWER(SIN((#orig_lon - longitude) * pi()/180 / 2), 2) )) as distance
FROM geo_kulplex.sweden_bobo
/* WHERE clause to pre-filter by distance approximation .. filter results
later with precise euclidian calculation. can use indexes. */
WHERE
/* i'm unsure about geo stuff ... i dont think you want a
distance of 10° here, please adjust this properly!! */
latitude BETWEEN (#orig_lat - #dist) AND (#orig_lat + #dist)
AND longitude BETWEEN (#orig_lon - #dist) AND (#orig_lon + #dist)
/* HAVING clause to filter result using the more precise euclidian distance */
HAVING distance < #dist
ORDER BY distance limit 10;
For those who are interested in the constant:
3956 is the radius of the earth in miles, so the resulting distance is measured in miles
6371 is the radius of the earth in kilometers, so use this constant to measure distance in kilometers
Find more information in the wiki about the Haversine formula